class Solution {//leetcode200——岛屿数量
private:
    int dx[4]={0,0,-1,1};
    int dy[4]={1,-1,0,0};
    void dfs(vector<vector<char>>& grid,int i,int j){
        vis[i][j]=true;
        for(int k=0;k<4;k++){
            int x=i+dx[k];
            int y=j+dy[k];
            if(x>=0&&x<m&&y>=0&&y<n&&grid[x][y]=='1'&&vis[x][y]==false){
                dfs(grid,x,y);
            }
        }
    }
public:
    int numIslands(vector<vector<char>>& grid) {
        m=grid.size();
        n=grid[0].size();
        vis.resize(m,vector<bool>(n,false));
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(grid[i][j]=='1'&&vis[i][j]==false){
                    dfs(grid,i,j);
                    ret++;
                }
            }
        }
        return ret;
    }
private:
    int ret=0;
    int m;
    int n;
    vector<vector<bool>> vis;
};